This invention relates to a variable valve timing gear for internal combustion engines of the type having intake and exhaust valves actuated by means of cams of a camshaft, some of which cams being rotatable relatively to other of the cams for controlling the valve overlap of the intake and exhaust valves with respect to one another.
As a result of variable valve timing gears, not only crude HC-emissions can be favorably influenced but NO.sub.x -emissions can also be reduced. These variable valve timing gears can also improve the fuel consumption, the idling stability, the torque and the output of an internal-combustion engine. For this purpose, valve overlaps of the intake and exhaust valves are changed in such a manner that, at low rotational speeds, there will be a relatively small overlap and, at higher rotational speeds, there will be a relatively large overlap.
According to US-SAE Paper 740 102, Page 2, FIG. 1, a variable valve timing gear is known in which an axially movable control element is provided in a bore of a camshaft and engages by means of a driver in a curved control guide causing a rotation of the intake cams. Although this construction supplies a vague constructional direction, it is still removed from a solution that can be implemented in practice.
Based on this prior art, it is therefore an object of the invention to provide an improved variable valve timing gear with intake cams and exhaust cams which can be rotated with respect to one another. This valve timing gear can be implemented without any problems and operates well.
This object is achieved according to preferred embodiments of the invention by providing a variable valve timing gear for an engine of piston-type construction comprising intake and exhaust valves for charge cycle control which are actuated by means of camshaft cams, some of which cams are rotatable for influencing the valve overlap of the intake and exhaust valves with respect to one another, said variable valve timing gear including a control arrangement which includes a control element which is axially movable in an axial bore of the camshaft, which control element causes rotational adjustment of the intake cams with respect to the exhaust cams via drivers and control guides, wherein the drivers are pins of the control element penetrating guide openings in the camshaft and engaging in grooves constructed as control guides in bearing bores of the intake cams which are rotatably disposed on the camshaft.
Principal advantages achieved by means of the invention are that the control element with its drivers, which engage in grooves of the intake cams, can not only be implemented easily from a constructional point of view but is also operationally reliable and highly effective with respect to the rotating function of the intake cams. In this case, the control element as well as the camshaft have a simple construction. The camshaft may be a so-called built or assembled camshaft on which the exhaust cam, bearing bushes or the like are fixed and the inlet cams are disposed in a rotatable manner. The control arrangement comprises a hydraulic system and a solenoid, is arranged on an end face of the camshaft which is favorable with respect to space and may optionally also be construction as a suppliable module which can be used, for example, as a variant with respect to a camshaft with fixed intake and exhaust valves in the case of engines which have the same construction but a different output profile. Finally, this type of camshaft adjustment is suitable for so-called single-camshaft internal-combustion engines in which the intake and the exhaust valves are arranged on a common shaft.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.